1. Field of the Invention
The invention lies in the field of endoluminal blood vessel repairs. The invention specifically relates to a method for making a non-circular stent, which can be used to endoluminally repair aneurysm and/or dissections of the thoracic transverse aortic arch, thoracic posterior aortic arch, and the descending thoracic portion of the aorta.
2. Description of the Related Art
A stent graft is an implantable device made of a tube-shaped surgical graft covering and an expanding or self-expanding frame. The stent graft is placed inside a blood vessel to bridge, for example, an aneurismal, dissected, or other diseased segment of the blood vessel, and, thereby, exclude the hemodynamic pressures of blood flow from the diseased segment of the blood vessel.
In selected patients, a stent graft advantageously eliminates the need to perform open thoracic or abdominal surgical procedures to treat diseases of the aorta and eliminates the need for total aortic reconstruction. Thus, the patient has less trauma and experiences a decrease in hospitalization and recovery times. The time needed to insert a stent graft is substantially less than the typical anesthesia time required for open aortic bypass surgical repair, for example.
Use of surgical and/or endovascular grafts have widespread use throughout the world in vascular surgery. There are many different kinds of vascular graft configurations. Some have supporting framework over their entirety, some have only two stents as a supporting framework, and others simply have the tube-shaped graft material with no additional supporting framework, an example that is not relevant to the present invention.
One of the most commonly known supporting stent graft frameworks is that disclosed in U.S. Pat. Nos. 5,282,824 and 5,507,771 to Gianturco (hereinafter collectively referred to as “Gianturco”). Gianturco describes a zig-zag-shaped, self-expanding stent commonly referred to as a z-stent. The stents are, preferably, made of nitinol, but also have been made from stainless steel and other biocompatible materials.
There are various features characterizing a stent graft. The first significant feature is the tube of graft material. This tube is commonly referred to as the graft and forms the tubular shape that will, ultimately, take the place the diseased portion of the blood vessel. The graft is, preferably, made of a woven sheet (tube) of polyester or PTFE. The circumference of the graft tube is, typically, at least as large as the diameter and/or circumference of the vessel into which the graft will be inserted so that there is no possibility of blood flowing around the graft (also referred to as endoleak) to either displace the graft or to reapply hemodynamic pressure against the diseased portion of the blood vessel. Accordingly, to so hold the graft, self-expanding frameworks are attached typically to the graft material, whether on the interior or exterior thereof. Because blood flow within the lumen of the graft could be impaired if the framework was disposed on the interior wall of the graft, the framework is connected typically to the exterior wall of the graft. The ridges formed by such an exterior framework help to provide a better fit in the vessel by providing a sufficiently uneven outer surface that naturally grips the vessel where it contacts the vessel wall and also provides areas around which the vessel wall can endothelialize to further secure the stent graft in place.
One of the significant dangers in endovascular graft technology is the possibility of the graft migrating from the desired position in which it is installed. Therefore, various devices have been created to assist in anchoring the graft to the vessel wall.
One type of prior art prosthetic device is a stent graft made of a self-expanding metallic framework. For delivery, the stent graft is, first, radially compressed and loaded into an introducer system that will deliver the device to the target area. When the introducer system holding the stent graft positioned in an appropriate location in the vessel and allowed to open, the radial force imparted by the self-expanding framework is helpful, but, sometimes, not entirely sufficient, in endoluminally securing the stent graft within the vessel.
U.S. Pat. No. 5,824,041 to Lenker et al. (hereinafter “Lenker”) discloses an example of a stent graft delivery system. Lenker discloses various embodiments in which a sheath is retractable proximally over a prosthesis to be released. With regard to FIGS. 7 and 8, Lenker names components 72 and 76, respectively, as “sheath” and “prosthesis-containment sheath.” However, the latter is merely the catheter in which the prosthesis 74 and the sheath 72 are held. With regard to FIGS. 9 and 10, the sheath 82 has inner and outer layers 91, 92 fluid-tightly connected to one another to form a ballooning structure around the prosthesis P. This ballooning structure inflates when liquid is inflated with a non-compressible fluid medium and flares radially outward when inflated. With regard to FIGS. 13 to 15, Lenker discloses the “sheath” 120, which is merely the delivery catheter, and an eversible membrane 126 that “folds back over itself (everts) as the sheath 120 is retracted so that there are always two layers of the membrane between the distal end of the sheath [120] and the prosthesis P.” Lenker at col. 9, lines 63 to 66. The eversion (peeling back) is caused by direct connection of the distal end 130 to the sheath 120. The Lenker delivery system shown in FIGS. 19A to 19D holds the prosthesis P at both ends 256, 258 while an outer catheter 254 is retracted over the prosthesis P and the inner sheath 260. The inner sheath 260 remains inside the outer catheter 254 before, during, and after retraction. Another structure for holding the prosthesis P at both ends is illustrated in FIGS. 23A and 23B. Therein, the proximal holder having resilient axial members 342 is connected to a proximal ring structure 346. FIGS. 24A to 24C also show an embodiment for holding the prosthesis at both ends inside thin-walled tube 362.
To augment radial forces of stents, some prior art devices have added proximal and/or distal stents that are not entirely covered by the graft material. By not covering with graft material a portion of the proximal/distal ends of the stent, these stents have the ability to expand further radially than those stents that are entirely covered by the graft material. By expanding further, the proximal/distal stent ends better secure to the interior wall of the vessel and, in doing so, press the extreme cross-sectional surface of the graft ends into the vessel wall to create a fixated blood-tight seal.
One example of such a prior art exposed stent can be found in United States Patent Publication US 2002/0198587 to Greenberg et al. The modular stent graft assembly therein has a three-part stent graft: a two-part graft having an aortic section 12 and an iliac section 14 (with four sizes for each) and a contralateral iliac occluder 80. FIGS. 1, 2, and 4 to 6 show the attachment stent 32. As illustrated in FIGS. 1, 2, and 4, the attachment stent 32, while rounded, is relatively sharp and, therefore, increases the probability of puncturing the vessel.
A second example of a prior art exposed stent can be found in U.S. Patent Publication 2003/0074049 to Hoganson et al. (hereinafter “Hoganson”), which discloses a covered stent 10 in which the elongated portions or sections 24 of the ends 20a and 20b extend beyond the marginal edges of the cover 22. See Hoganson at FIGS. 1, 3, 9, 11a, 11b, 12a, 12b, and 13. However, these extending exposed edges are triangular, with sharp apices pointing both upstream and downstream with regard to a graft placement location. Such a configuration of the exposed stent 20a, 20b increases the possibility of puncturing the vessel. In various embodiments shown in FIGS. 6a, 6b, 6c, 10, 14a, Hoganson teaches completely covering the extended stent and, therefore, the absence of a stent extending from the cover 22. It is noted that the Hoganson stent is implanted by inflation of a balloon catheter.
Another example of a prior art exposed stent can be found in U.S. Pat. No. 6,565,596 to White et al. (hereinafter “White I”), which uses a proximally extending stent to prevent twisting or kinking and to maintain graft against longitudinal movement. The extending stent is expanded by a balloon and has a sinusoidal amplitude greater than the next adjacent one or two sinusoidal wires. White I indicates that it is desirable to space wires adjacent upstream end of graft as close together as is possible. The stent wires of White I are actually woven into graft body by piercing the graft body at various locations. See White I at FIGS. 6 and 7. Thus, the rips in the graft body can lead to the possibility of the exposed stent moving with respect to the graft and of the graft body ripping further. Between the portions of the extending stent 17, the graft body has apertures.
The stent configuration of U.S. Pat. No. 5,716,393 to Lindenberg et al. is similar to White I in that the outermost portion of the one-piece stent—made from a sheet that is cut/punched and then rolled into cylinder—has a front end with a greater amplitude than the remaining body of the stent
A further example of a prior art exposed stent can be found in U.S. Pat. No. 6,524,335 to Hartley et al. (hereinafter “Hartley”). FIGS. 1 and 2 of Hartley particularly disclose a proximal first stent 1 extending proximally from graft proximal end 4 with both the proximal and distal apices narrowing to pointed ends.
Yet another example of a prior art exposed stent can be found in U.S. Pat. No. 6,355,056 to Pinheiro (hereinafter “Pinheiro I”). Like the Hartley exposed stent, Pinheiro discloses exposed stents having triangular, sharp proximal apices.
Still a further example of a prior art exposed stent can be found in U.S. Pat. No. 6,099,558 to White et al. (hereinafter “White II”). The White II exposed stent is similar to the exposed stent of White I and also uses a balloon to expand the stent.
An added example of a prior art exposed stent can be found in U.S. Pat. No. 5,871,536 to Lazarus, which discloses two support members 68 longitudinally extending from proximal end to a rounded point. Such points, however, create a very significant possibility of piercing the vessel.
An additional example of a prior art exposed stent can be found in U.S. Pat. No. 5,851,228 to Pinheiro (hereinafter “Pinheiro II”). The Pinheiro II exposed stents are similar to the exposed stents of Pinheiro I and, as such, have triangular, sharp, proximal apices.
Still another example of a prior art exposed stent can be found in Lenker (U.S. Pat. No. 5,824,041), which shows a squared-off end of the proximal and distal exposed band members 14. A portion of the exposed members 14 that is attached to the graft material 18, 20 is longitudinally larger than a portion of the exposed members 14 that is exposed and extends away from the graft material 18, 20. Lenker et al. does not describe the members 14 in any detail.
Yet a further example of a prior art exposed stent can be found in U.S. Pat. No. 5,824,036 to Lauterjung, which, of all of the prior art embodiments described herein, shows the most pointed of exposed stents. Specifically, the proximal ends of the exposed stent are apices pointed like a minaret. The minaret points are so shaped intentionally to allow forks 300 (see Lauterjung at FIG. 5) external to the stent 154 to pull the stent 154 from the sheath 302, as opposed to being pushed.
A final example of a prior art exposed stent can be found in U.S. Pat. No. 5,755,778 to Kleshinski. The Kleshinski exposed stents each have two different shaped portions, a triangular base portion and a looped end portion. The totality of each exposed cycle resembles a castellation. Even though the end-most portion of the stent is curved, because it is relatively narrow, it still creates the possibility of piercing the vessel wall.
All of these prior art stents suffer from the disadvantageous characteristic that the relatively sharp proximal apices of the exposed stents have a shape that is likely to puncture the vessel wall.
Devices other than exposed stents have been used to inhibit graft migration. A second of such devices is the placement of a relatively stiff longitudinal support member longitudinally extending along the entirety of the graft.
The typical stent graft has a tubular body and a circumferential framework. This framework is not usually continuous. Rather, it typically takes the form of a series of rings along the tubular graft. Some stent grafts have only one or two of such rings at the proximal and/or distal ends and some have many stents tandemly placed along the entirety of the graft material. Thus, the overall stent graft has an “accordion” shape. During the systolic phase of each cardiac cycle, the hemodynamic pressure within the vessel is substantially parallel with the longitudinal plane of the stent graft. Therefore, a device having unsecured stents, could behave like an accordion or concertina with each systolic pulsation, and may have a tendency to migrate downstream. (A downstream migration, to achieve forward motion, has a repetitive longitudinal compression and extension of its cylindrical body.) Such movement is entirely undesirable. Connecting the stents with support along the longitudinal extent of the device thereof can prevent such movement. To provide such support, a second anti-migration device can be embodied as a relatively stiff longitudinal bar connected to the framework.
A clear example of a longitudinal support bar can be found in Pinheiro I (U.S. Pat. No. 6,355,056) and Pinheiro II (U.S. Pat. No. 5,851,228). Each of these references discloses a plurality of longitudinally extending struts 40 extending between and directly interconnecting the proximal and distal exposed stents 20a, 20b. These struts 40 are designed to extend generally parallel with the inner lumen 15 of the graft 10, in other words, they are straight.
Another example of a longitudinal support bar can be found in U.S. Pat. No. 6,464,719 to Jayaraman. The Jayaraman stent is formed from a graft tube 21 and a supporting sheet 1 made of nitinol. This sheet is best shown in FIG. 3. The end pieces 11, 13 of the sheet are directly connected to one another by wavy longitudinal connecting pieces 15 formed by cutting the sheet 1. To form the stent graft, the sheet 1 is coiled with or around the cylindrical tube 21. See FIGS. 1 and 4. Alternatively, a plurality of connecting pieces 53 with holes at each end thereof can be attached to a cylindrical fabric tube 51 by stitching or sutures 57, as shown in FIG. 8. Jayaraman requires more than one of these serpentine shaped connecting pieces 53 to provide longitudinal support.
United States Patent Publication 2002/0016627 and U.S. Pat. No. 6,312,458 to Golds each disclose a variation of a coiled securing member 20.
A different kind of supporting member is disclosed in FIG. 8 of U.S. Pat. No. 6,053,943 to Edwin et al.
Like Jayaraman, U.S. Pat. No. 5,871,536 to Lazarus discloses a plurality of straight, longitudinal support structures 38 attached to the circumferential support structures 36, see FIGS. 1, 6, 7, 8, 10, 11, 12, 14. FIG. 8 of Lazarus illustrates the longitudinal support structures 38 attached to a distal structure 36 and extending almost all of the way to the proximal structure 36. The longitudinal structures 38, 84, 94 can be directly connected to the body 22, 80 and can be telescopic 38, 64.
United States Patent Publication 2003/0088305 to Van Schie et al. (hereinafter “Van Schie”) does not disclose a support bar. Rather, it discloses a curved stent graft using an elastic material 8 connected to stents at a proximal end 2 and at a distal end 3 (see FIGS. 1, 2) thereof to create a curved stent graft. Because Van Schie needs to create a flexible curved graft, the elastic material 8 is made of silicone rubber or another similar material. Thus, the material 8 cannot provide support in the longitudinal extent of the stent graft. Accordingly, an alternative to the elastic support material 8 is a suture material 25 shown in FIGS. 3 to 6.